OPA197_16 Datasheet, PDF (20/39 Pages) Texas Instruments – 36-V, Precision, Rail-to-Rail Input/Output, Low Offset Voltage Operational Amplifiers

OPA197, OPA2197, OPA4197
SBOS737A – JANUARY 2016 – REVISED JULY 2016
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7.3 Feature Description
7.3.1 Input Protection Circuitry
The OPAx197 uses a unique input architecture to eliminate the need for input protection diodes, but still provides
robust input protection under transient conditions. Conventional input diode protection schemes shown in
Figure 41 can be activated by fast transient step responses and can introduce signal distortion and settling time
delays because of alternate current paths, as shown in Figure 42. For low-gain circuits, these fast-ramping input
signals forward-bias back-to-back diodes, causing an increase in input current, and resulting in extended settling
time, as shown in Figure 43.
V+
V+
+IN
+IN
OUT
OUT
36 V
OPAx197
~0.7 V
-IN
-IN
V
OPAx197 Provides Full 36-V
Differential Input Range
V
Conventional Input Protection
Limits Differential Input Range
Figure 41. OPA197 Input Protection Does Not Limit Differential Input Capability
Vn = +10 V R_FILT
+10 V
C_FILT
Vn+1 = ±10 V R_FILT
±10 V
C_FILT
Input Low Pass Filter
S_n
C_S
R_{on_mux}
1
D
1
2
+10 V
~±9.3 V
C_D
S_n+1
R_{on_mux}
2
Vin±
C_S
I_{diode_transient}
~0.7 V
Vin+
±10 V
Vout
Simplified Mux Model
Buffer Amplifier
Figure 42. Back-to-Back Diodes Create Settling Issues
100
Op amp with standard input diodes
OPA197
50
0
0.1% settling = r10 mV
-50
-100
0
6 12 18 24 30 36 42 48 54 60
Time (Ps)
Figure 43. OPA197 Protection Circuit Maintains Fast-Settling Transient Response
20
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